Test equipment is used to evaluate the performance of integrated circuits prior to shipment to customers. Among other things, test equipment typically includes a number of “pin cards” that each have circuitry for communicating with a corresponding pin of the integrated circuit being tested (referred to in the art as “device under test”, or “DUT”). Each pin card may include one or more “pin drivers” for transmitting a test signal to a corresponding pin on the DUT. The pin driver is typically connected to the corresponding pin via a relatively short transmission line.
The pin driver is commonly used in ATE (automatic test equipment) systems as both a driver and as a high quality AC termination. When the pin driver is used as a driver, the output stage has dedicated slew currents which are available for switching between vhigh and vlow levels, and in some cases to a third vterm level. When used as a termination, the pin driver provides a matched impedance to the transmission line which carries the signal from the device under to test to the pin electronics. Prior art drivers have incorporated class AB output stages with two levels (vhigh and vlow) or three levels (vhigh, vlow, and vterm). In each active level, the driver input and output stages remain fully powered up to enable high speed switching between levels. In some applications, this approach results in excessive power consumption.